T-Mobile US Inc is considering buying spectrum from an unidentified private party and would use some of the proceeds of a planned $2 billion share offering to finance such a deal, the company said in a regulatory filing on Tuesday.

On Monday, after the market close, the company announced an offering of up to roughly 72 million shares and said it could buy wireless airwaves using proceeds from the sale. The share sale could represent the fourth biggest secondary offering so far this year, according to Reuters data.

T-Mobile (Bellevue, WA, USA), the No. 4 U.S. mobile operator, said in the filing that it would not participate in a spectrum auction the U.S. government plans to hold in January, leaving investors in suspense over what spectrum it is looking to buy.

T-Mobile shares were down almost 2 percent at $26.44 on the New York Stock Exchange as investors worried that the share offering could dilute the value of T-Mobile shares.

Deutsche Telekom (Bonn, Germany), which owns 74 percent of T-Mobile, said its stake would be reduced to 67 percent as a result of the offering.